Coherent optical system comprising a tunable local oscillator

ABSTRACT

A method and an optical network component for data processing in an optical network. A first signal and a second signal are influenced by a tunable element. The first signal is an incoming optical signal, and the second signal is a local oscillator signal generated by a laser. The laser has an optical gain element that is tuned by the tunable element. A communication system is provided with the optical network component.

The invention relates to a method and to an optical network component for data processing in an optical network and to a communication system comprising such optical network compovent.

A passive optical network (PON) is a promising approach regarding fiber-to-the-home (FTTH), fiber-to-the-business (FTTB) and fiber-to-the-curb (FTTC) scenarios, in particular as it overcomes the economic limitations of traditional point-to-point solutions.

The PON has been standardized and it is currently being deptoyed by network service providers worldwide. Conventional PONS distribute downstream traffic from the optical line terminal (OLT) to optical network units (ONUs) in a broadcast manner while the ONUs send upstream data packets multiplexed in time to the OLT. Hence, communication among the ONUs needs to be conveyed through the OLT involving electronic processing such as buffering and/or scheduling, which results in latency and degrades the throughput of the network.

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber.

WDM systems are divided into different wavelength patterns, conventional or coarse and dense WDM. WDM systems provide, e.g., up to 16 channels in the 3rd transmission window (Cband) of silica fibers around 1550 nm. Dense WDM uses the same transmission window but with denser channel spacing. Channel plans vary, but a typical system may use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing. Some technologies are capable of 25 GHz spacing. Amplification options enable the extension of the usable wavelengths to the L-band, more or less doubling these numbers.

Optical access networks, e.g., a coherent Ultra-Dense Wavelength Division Multiplex (UDWDM) network, are deemed to be the future data access technology.

Within the UDWDM concept, potentially all wavelengths are routed to each ONU. The respective wavelength is selected by the tuning of the local oscillator (LO) laser at the ONU. Other wavelengths also arriving at the ONT result in an optical offset and increase the noise of the signal to be detected. A sufficiently strong LO renders the contributions of such other wavelengths minor compared to the signal itself.

The problem to be solved is to overcome the disadvantages as described above and in particular to allow for an efficient optical signal processing.

This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims.

In order to overcome this problem, a method for data processing in an optical network is provided,

-   -   wherein a first signal and a second signal are influenced by a         tunable element;     -   wherein the first signal is an incoming optical signal;     -   wherein the second signal is a local oscillator signal generated         by a laser;     -   wherein said laser comprises an optical gain element that is         tuned by the tunable element.

Hence, contributions of the other wavelengths arriving at an optical network element, e.g., an ONU or an OLT, could be efficiently suppressed thereby increasing both the receiver's sensitivity and the signal-to-noise ratio.

In a further embodiment, said laser is adjusted by the tunable element for receiving the first signal.

In a next embodiment, the tunable element is a filter, in particular a dielectric filter.

It is also an embodiment that the tunable element is an angle-tunable element.

The tunable element may in particular be a mechanical and/or electrical component influencing the first signal and the second signal via a single adjustment.

Pursuant to another embodiment, the first signal and the second signal are conveyed via waveguides, wherein said waveguides are offset to each other.

In case the waveguides are arranged offset to one another, e.g., crosstalk can be efficiently reduced or avoided.

According to an embodiment, said tunable element provides a mechanical and/or an electrical coupling for influencing the first signal and the second signal.

In particular, a single adjustment of the tunable element has an impact on the first signal and on the second signal.

According to another embodiment, said method is processed in an optical network element, in particular in an ONU and/or in an OLT.

According to a further embodiment, said optical gain element is a laser diode in particular comprising an anti-reflection coating.

According to a further embodiment, the optical gain element comprises or is associated with a semiconductor optical amplifier (SOA).

According to yet an embodiment, the optical gain element comprises or is associated with a modulator.

It is also an embodiment that the first signal is combined with and/or fed to the second signal.

This efficiently allows for a coherent reception in particular within an OLT or an ONU.

The problem stated above is also solved by an optical network component comprising a tunable element for influencing a first signal and a second signal in particular via a mechanical and/or an electrical coupling, wherein the first signal is an incoming optical signal and wherein the second signal is a local oscillator signal generated by a laser, wherein said laser comprises an optical gain element that is tuned by the tunable element.

Said optical network component may be any device or component comprising an optical function that could be used in an optical network.

According to an embodiment, the optical component is or is associated with an ONU and/or with an OLT.

According to a further embodiment, the optical network compovent comprises a laser for providing a local oscillator signal.

According to yet an embodiment, said tunable element is a filter, in particular an angle-tunable dielectric filter.

The problem stated supra is further solved by a communication system comprising the optical network component as described herein.

Embodiments of the invention are shown and illustrated in the following figures:

FIG. 1 shows a diagram depicting the basic principle of a filter that has an impact on an incoming data signal as well as on a local oscillator signal provided by a laser;

FIG. 2 shows an alternative embodiment as how an incoming and an outgoing signal may be influenced by a single tunable element, e.g., a filter.

The approach provided herein enables a tunable element of an optical component to be used for filtering purposes.

Said tunable element may in particular be or comprise a dielectric filter that determines the wavelength of a local oscillator (LO).

FIG. 1 shows an optical gain element 106 (e.g., a laser active medium) providing an optical signal via a waveguide 105 and a lens 104 to a filter 103, which is in particular an angle-tunable dielectric filter. The combination of said filter 103 and the optical gain element 106 comprising a mirror 107 constitutes a tunable laser 108, i.e. the tunable laser 108 can be adjusted via said filter 103.

On the other hand, a data signal is conveyed via a waveguide 101 to a circulator 102, which feeds the data signal towards the filter 103 and the reflection or signal provided by the filter 103 to a splitter 109. The splitter 109 supplies its input signal to a modulator 111 and further via a fiber (not shown) to a remote receiver as well as to a local receiver 110 for further processing purposes.

Hence the filter 103 has an impact on the data signal conveyed via the circulator 102 as well as on the signal provided by the optical gain element 106.

The filter 103 may serve as a mirror for the laser 106 and the back side of the filter 103 may serve as a mirror for the data signal.

The filter 103 may provide a physical impact due to its positioning to both, the LO signal as well as the data signal.

Hence, the filter 103 can be used for selecting and/or adjusting the wavelength of the LO as well as it can be used for filtering the incoming data signal. In particular, the signal wavelength required (including, e.g., some (few) neighboring channels) is reflected by said filter 103.

In case the tunable laser 108 is adjusted by moving the angle of the filter 103, the data signal as well as the LO signal provided by the tunable laser 108 are adjusted accordingly, i.e. dependent on such movement or position of the filter 103.

Advantageously, the wavelength of the data signal and the wavelength of the laser signal (LO signal) can be automatically aligned by said filter without any need for additional elements or components.

In case the incoming data signal is too strong and the wavelength passing the filter 103 may have an impact on the optical gain element 106, the signal waveguide 101 and the laser waveguide 105 could be arranged in a slightly offset way to avoid such effect. In addition, cross-talk could be reduced or avoided by such offset arrangement of the waveguides 101 and 105.

It is a further advantage that an integrated photonic circuit can be used thus gaining receiver sensitivity.

The arrangement shown in FIG. 1 can be provided with an optical network component, e.g., with an OLT or an ONU.

FIG. 2 shows an exemplary arrangement as how an incoming and an outgoing signal may be influenced by a single tunable element, e.g., a filter.

An optical gain element 201 comprises a Semiconductor Optical Amplifier (SOA) 205 via which a signal is being conveyed towards a filter 203 and reflected by a mirror (or reflector) 204 back to the optical gain element 201. Hence, the filter 203 can be used to adjust a wavelength of a laser. The optical gain element 201 comprises a mirror 202 that is used to reflect the incoming signal from the filter 203 to be modulated by a modulator 209 and provided as an output signal “Signal Out” 207.

It is noted that the optical gain element may be a laser diode comprising an anti-reflection coating.

In addition, an input signal (data signal, “Signal In” 210) can be fed via the filter 203 to a photodiode 208.

The filter 203 may be realized as a mechanical component comprising a rotational axis 206 such that the impact to the signal generated by the laser 201 and the input signal corresponds to the positioning or movement of said filter.

The filter 203 can be adjusted by a piezo-electric actuator, e.g. a motor or the like.

Furthermore, the signal conveyed from the optical gain element 201 towards the mirror 204 may in addition be utilized and/or combined with the input signal “Signal In” 210 to allow for a coherent reception.

LIST OF ABBREVIATIONS

-   OLT Optical Line Terminal -   ONU Optical Network Unit -   PD Photo Diode -   PON Passive Optical Network -   SOA Semiconductor Optical Amplifier -   UDWDM Ultra Dense WDM -   WDM Wavelength Division Multiplex 

1-15. (canceled)
 16. A method of data processing in an optical network, which comprises the following steps: receiving a first signal in the form of an incoming optical signal; providing a second signal in the form of a local oscillator signal generated by a laser; influencing the first signal and the second signal with a tunable element; and providing the laser with an optical gain element and tuning the optical gain element of the laser with the tunable element.
 17. The method according to claim 16, which comprises adjusting the laser by the tunable element for receiving the first signal.
 18. The method according to claim 16, wherein the tunable element is a filter.
 19. The method according to claim 18, wherein the tunable element is a dielectric filter.
 20. The method according to claim 16, wherein the tunable element is an angle-tunable element.
 21. The method according to claim 16, which comprises conveying the first signal and the second signal via waveguides, wherein the waveguides are offset to each other.
 22. The method according to claim 16, wherein said tunable element comprises a mechanical and/or an electrical coupling for influencing the first signal and the second signal.
 23. The method according to claim 16, which comprises carrying out the method steps in an optical network element.
 24. The method according to claim 23, wherein the optical network element is at least one of an optical network unit and an optical line terminal.
 25. The method according to claim 16, wherein the optical gain element is a laser diode.
 26. The method according to claim 25, wherein the laser diode comprises an anti-reflection coating.
 27. The method according to claim 16, wherein the optical gain element comprises or is associated with a semiconductor optical amplifier.
 28. The method according to claim 16, wherein the optical gain element comprises or is associated with a modulator.
 29. The method according to claim 16, which comprises combining the first signal with the second signal and/or feeding the first signal to the second signal.
 30. An optical network component, comprising: a laser having an optical gain element; a tunable element for influencing a first signal and a second signal, the first signal being an incoming optical signal and the second signal being a local oscillator signal generated by said laser; and wherein said optical gain element of said laser is tuned by said tunable element.
 31. The optical network component according to claim 30, wherein said tunable element is configured to influence the first and second signals via mechanical and/or electrical coupling.
 32. The optical network component according to claim 30, configured as an optical network unit or as an optical line terminal.
 33. The optical network component according to claim 30 in combination with an optical network unit or an optical line terminal.
 34. The optical network component according to claim 30, wherein said tunable element is a filter.
 35. The optical network component according to claim 34, wherein said tunable element is an angle-tunable dielectric filter.
 36. A communication system, comprising the optical network component according claim
 30. 